What do you think? What should I improve? I know there are vertices that have more than 4 edges colliding, how can I avoid this in the future? I think it was an improvement though: From 97,734 tris and 147,480 edges (after decimating, formerly >1 M) to 5,262 faces and 5,264 verts (Without subdivision surface) P.D.: In the original shape, eyes were another mesh.
Overall I think it looks better. I think a good resource is to just Google face retopology and see how others lay out their loops. Watching a time lapse is also great. Just try to keep practicing. Start creating edges, around the extremes points of your mesh, and think in advance how you’ll connect them.
I see that in middle of the face there are some triangles. Also on the checks, the flow of edges seem to just stop and accumulate in that area. You may have to get a little clever if you encounter a tri or n-gon, utilizing your knife tool, merging, ect.
There are some excellent YouTube videos about topology that will give you good insight on topology fundamentals.
Oh dear,
That is not good...(but don't panic!)
Did you really place those Vertices by hand, or did you use a tool?
Head retopology is not easy and it might not be the best place to start your first attempt.
But the HUMAN Course here on CGCookie has a great head retopology part...(even for beginners, I think)...Although I'd recommend starting with some basics:
https://cgcookie.com/courses/introduction-to-retopology
Vertices with more than 4 Edges connected to it (poles) are not completely avoidable in heads, but try not to get more than 5 Edges per Vertex.
There are some guidelines for making good face topology, but if you let an experienced artist retopologize the same sculpt more than once, the result will probably be different each time...
Please don't be discouraged, you'll get there!
Thank you both for your encouragement cchrisnelson33 and 
spikeyxxx... I did this without any previous knowledge, trusting my gut instinct and well, this came out! hhahaha. I did use a tool but, as stated, this was my first attemp (without watching any tutorials, thus the fail) but it was a fun, but tedious, experiment. In the future I'll tackle this with more guidance. Stay tuned till my next retopo, this time following your advice.
JL goes through a beginners version of that in the modeling boot camp:
https://cgcookie.com/lessons/modeling-a-head-pt-1-main-loops